1. Field of the Invention
The present invention relates to a flat type vibration motor, more particularly, which is so structured to prevent any stoppage in the initialization or operation thereof to realize efficient and stable initialization and operation. The present invention also relates to a flat type vibration motor capable of incorporating a single winding coil therein to simplify an assembly process thereby saving labor cost and material cost as well as simplify an assembly structure thereby saving manufacturing cost.
2. Description of the Related Art
Communication instruments generally use bells and vibrators to inform users of call incoming. In a vibration mode, a small-sized vibration motor is typically operated to transfer driving force to a housing of a communication instrument thereby vibrating the whole communication equipment.
A vibration motor applied to the communication instrument such as a mobile phone is classified into a flat type (or a coin type) vibration motor and a cylinder type (or a bar type) vibration motor.
The flat type vibration motor facilitates the miniaturization of mobile phone parts because it can be fabricated in a relatively thin and simple structure for generating vibration, for example, in which a weight is placed inside the motor to be rotated along with a rotor. Owing to these advantages, the coverage of the flat type vibration motor is gradually increasing.
FIG. 1 is a longitudinal sectional view of a general flat type vibration motor. As shown in FIG. 1, a conventional flat type motor 1 generally includes a rotor member or a rotor assembly (hereinafter will be referred to as “rotor”) 10, a stationary member or stator assembly (hereinafter will be referred to as “stator”) 20 and a housing 30 containing both the rotor 10 and the stator 20.
The rotor 10 is of an eccentric rotational structure which is rotatably assembled within the housing 30, and has coils 12 and 14 of wires wound around cores by a number of times, respectively, on a top board 11 without a pattern circuit and a weight 13 eccentrically arranged adjacent to the winding coils 12 and 14. The winding coils 12 and 14 and the weight 13 are molded within an insulation material 16, which is insert molded to protect the winding coils 12 and 14 and the weight 13 from the external environment.
The rotor 10 also has a rectifier 15 on the underside of the top board 11, in which the rectifier 15 is radially divided into a plurality of segments 15a to 15d at a predetermined gap and has a contact face exposed downward. Some of the segments 15a to 15d of the rectifier 15 perform elastic contact with the upper ends of the positive and negative brush fingers 25a and 25b of a brush 25 arranged in a stator 20.
The stator 20 is of a fixed structure arranged on a bracket 35 which is assembled to the housing 30 to close the opened bottom of the housing 30. In the stator 20, a rim-shaped magnet 22 of N and S poles radially alternating with each other is arranged on a bottom board 21 placed on the bracket 35, and a power supply 23 for electrically connecting the brush 25 with lead wires 24a and 24b for supplying external voltage includes positive and negative terminals 23a and 23b that are arranged on an upper face portion of the bottom board 21.
The brush 25 is divided into the positive and negative brush fingers 25a and 25b, which are electrically connected to the positive terminal 23a and the negative terminal 23b of the power supply 23, respectively, so as to be supplied with positive and negative voltages of different polarity, respectively.
Next, a shaft 31 erected from the top center of the bracket 35 is inserted into the rotor 10, and rotatably assembled to the rotor 10 via a bearing member 32 that is integral to the rotor 10. The shaft 31 is supported by upper and lower ends to the underside of the housing 30 and the top of the bracket 35, respectively.
In the operation of the vibration motor 1 of the above structure, an input voltage from the power supply 23 of the stator 20 is supplied to the rectifier 15 via the brush 25. More specifically, the voltage is alternatingly supplied to the winding coils 12 and 14 through the selective contact between the brush 25 divided into the positive and negative brush fingers and the rectifier 15 divided into plural parts corresponding to the brush 25.
The interaction between the winding coils 12 and 14 and the magnet 22 drives the rotor 10 to rotate about the shaft 31 in a predetermined direction. At this time, the rotor 10 eccentrically rotates about the shaft 31 generating lateral pressure, which in turn is transmitted in the form of vibration to the housing 30 and the bracket 35 that support the shaft 31 at the top and bottom so that a user can feel call incoming.
According to a conventional method for powering the winding coils 12 and 14 through the contact between the brush fingers 25a and 25b of the brush 25 and the segments 15a to 15d of the rectifier 15 to operate the motor as above, it is required to align the positive and negative brush fingers 25a and 25b steadily and correctly with segments 15a and 15c connected to both ends of the winding coil 12 and the segments 15b and 15d connected to both ends of the winding coil 14, respectively, according to an electrical angle θ determined by the number of the segments 15a to 15d. 
However, in the initialization or operation of the vibration motor of the above structure, if any one (for example 25b) of the positive and negative brush fingers 25a and 25b is offset from the preset electrical angle θ to contact any adjacent segment 15b or 15d as shown in dotted lines instead of contacting the segment 15c, thereby opening the electric circuit for electrically connecting the winding coils 12 and 14. Then, a dead point as an electrically disconnected section for temporarily interrupting power supply takes place to bring a temporary or complete stoppage to the initialization or operation of the motor, thereby producing a fatal problem of disabling the motor.
Such stoppage may be induced from defective assembly processes or design errors hindering the rectifier 15 and the brush 25 from being precisely assembled so that the segments 15a to 15d fail to steadily perform uniform contact with the brush fingers 25a and 25b at a predetermined electrical angle of 90 or 180°. Otherwise, the stoppage may take place in case that the brush 25 is deformed under the impact while passing through respective gaps defined by the segments 15a to 15d so as to change the contact position with respect to the rectifier 15.
As a consequence, there is proposed a conventional scheme as shown in FIG. 3 in order to prevent the stoppage of the motor originated from the dead point, by which the winding coils 12 are provided with double coils 12a, 12b, 14a and 14b, respectively, and the series-connected coils 12a and 12b are wired with the series-connected coils 14a and 14b to have a neutral point N at a common connection point thereof to provide an electric circuit capable of maintaining electric connection without a dead point even though the positive and negative brush fingers 25a and 25b are offset from the preset electrical angle θ.
However, according the conventional scheme of forming the neutral point N through the double winding of the winding coils 12 and 14, respectively, to prevent the dead point, because the winding coils 12 and 14 are double-wound with a winder (not shown), and then the double coils 12a, 12b, 14a and 14b of the winding coils 12 and 14 are necessarily arranged by a worker, the winding and arranging operations become very troublesome to degrade workability as well as increase coil consumption thereby to raise manufacturing cost.